1. Field of the Invention
The present invention relates generally to drain extended metal oxide semiconductor (DEMOS) transistors and, more specifically, to configurations for increasing the breakdown voltage of DEMOS transistors and methods for fabricating such transistors.
2. Description of the Related Art
The following descriptions and examples are given as background information only.
A transistor structure often used for high voltage applications (i.e., VDD>5 volts) is a drain extended metal oxide semiconductor (DEMOS) transistor, which may also be referred to in the microelectronics industry as a laterally diffused metal oxide semiconductor (LDMOS) transistor. DEMOS transistors differ from other MOS transistors in that the drain contact region is laterally displaced apart from the channel of the transistor at a greater distance than the source contact region of the transistor. As a consequence of the additional voltage drop in the drain extension region, the voltage across the channel of the DEMOS transistor is lower than a transistor having a drain contact region closer to the channel and, in turn, the electric field across the gate oxide is lower. As a result, DEMOS transistors are effective for operations at high voltage levels. As with all types of transistors, the maximum voltage level a DEMOS transistor may be configured to handle depends on the breakdown voltage of the transistor. Due to their general design layout, a DEMOS transistor may be limited to the type high voltage applications (e.g., VDD<15 volts) in which it may be used.
Accordingly, it would be beneficial to develop a DEMOS transistor with a relatively higher breakdown voltage.